The present invention relates to a fuel processor for generating hydrogen rich gas from hydrocarbon fuel comprising an inner housing having a fuel processor inlet for introducing hydrocarbon fuel into the inner housing and a fuel processor outlet for providing hydrogen rich gas for operating a fuel cell. In the inner housing, at least a fuel reformer unit for reforming hydrocarbon fuel to a hydrogen rich gas and optionally a gas cleaning unit for cleaning the hydrogen rich gas produced by the fuel reformer from unwanted by-products are arranged.
The present invention further relates to a method for operating such a fuel processor.
From the state of the art, e.g. EP 1 057 780, a fuel processor is known, where the reformer unit and subsequent gas cleaning units are integrated into a housing for providing a fuel processor reduced in size. This state of the art further discloses that the reforming section has a front side and a rear side which are separated by a bending section of 180°. Additionally, an insulation layer is formed around the reforming section which is constructed as a double layered structure. The space there between can be filled with a heating catalyst such as iron, copper or zinc, which generates heat by oxidation, when air is supplied to the heating catalyst.
Further, an air supply pipe is provided, which can supply air to the heating catalysts, and a deoxidizing gas supply is provided for leading a deoxidizing gas to the catalyst for terminating the heating. Additionally, a discharge pipe is provided for discharging air and deoxidizing gas, respectively.
By providing deoxidizing gas, such as fuel gas to the heating catalysts the heating of the reformer section can be terminated. This termination takes place as soon as a temperature sensor has sensed that the reformer section has gained its operating temperature.
The disclosed fuel reformer has the disadvantage that not only an oxidizing/deoxidizing gas supply and a discharge possibility needs to be provided, but also the oxidation needs to be stopped by deoxidizing gas. Further, the heating catalysts, namely copper, iron or zinc, increase the overall weight of the fuel reformer. Besides the increased weight, the heat production of the heating catalysts is often not sufficient for bringing the reformer section to operating temperatures of around 800° C. within an acceptable time period.
A further disadvantage of the disclosed fuel reformer is that heat generated during a normal operation of the reformer section cannot be used or transported off, whereby the temperature of the operating fuel processor cannot be regulated.
It is therefore desirable to provide a fuel processor, which provides a simple and effective preheating and a temperature regulating possibility of the fuel processor.
It is also desirable to provide an operating method for a fuel processor, which provides an effective and fast start-up phase of the fuel processor.
Aspects of the invention include a fuel processor, as well as a method for generating hydrogen rich gas.
An aspect of the invention is based on the idea to provide a fuel processor having an inner housing and an outer housing between which a mantel space is defined. The fuel processor further comprises at least one fuel reformer for generating a hydrogen rich gas from hydrocarbon fuel. Optionally, the fuel processor also comprises one or a plurality of gas cleaning units, which are supposed to remove unwanted by-products, such as carbon monoxide, from the generated hydrogen rich gas. Depending on the number and nature of the gas cleaning units and possible further processing units the hydrogen rich gas eventually is converted in a well-known manner into hydrogen gas with a purity required for the respective consumer of the hydrogen, e.g. for the operation of a fuel cell.
Into the mantel space a heat transporting fluid, preferably air, is introduced. A heat transporting fluid in the sense of the invention is any fluid, which is capable of picking up heat at one place and delivering heat to another place. According to a preferred embodiment of the invention, the heat transporting fluid streams from its inlet near the fuel processor outlet to fluid connection openings in the inner housing, which are arranged near the fuel processor inlet. The heat transporting fluid enters the inner housing through the fluid connection openings, mixes with hydrocarbon fuel and streams down to the fuel processor outlet inside the inner housing along with the reformed hydrogen rich gas.
According to an aspect of the invention, the flow direction of the heat transporting fluid during normal operation of the fuel processor is from the heat transporting fluid inlet through the fluid connection openings to the fuel processor outlet. Under the start-up condition of the fuel processor, the flow direction of the heat transporting fluid is reversed, so that the heat transporting fluid enters the inner housing through the fuel processor outlet, streams through the fluid connection openings from the inner housing into the mantel space and leaves the mantel space through the heat transporting fluid inlet. This inventive reversed fluid flow provides a possibility to accelerate the start-up process by providing a fast and effective preheating of the fuel processor.
By the use of a heat transporting fluid, which can be introduced into the inner space of the inner housing and which does not affect the reforming process, no additional discharging supply (as the one known from the state of the art) is needed. Such a heat transporting fluid is e.g. air. The use of air has the further advantage that air needs to be introduced into the inner housing anyhow, as air is necessary for the heating of the fuel reformer. For heating the fuel reformer a small part of the hydrocarbon fuel, which shall be reformed, and ideally all oxygen (from air) are burned, whereby the fuel reformer is kept on its operating temperature between 600° C. and 900° C. Since the air respectively the heat transporting fluid is guided along the outside of the fuel reformer, the fluid also serves as insulation for the fuel reformer. Thereby, no additional insulation is needed, so that the overall costs of the fuel processor can be reduced.
In a further preferred embodiment, the fluid inlet into the outer housing is arranged near the fuel processor outlet, whereby the heat transporting fluid can stream from the cool fluid processor outlet side to the hot reforming section of the fuel processor, whereby it can pick up and transport heat.
In a further preferred embodiment at least one fuel injection nozzle is arranged near the fuel processor inlet for injecting fuel into the mantel space. This fuel can be mixed with air and be ignited, preferably by a spark plug, so that the generated heat heats the reformer section of the fuel processor. The generated high temperature of the burning process can be used to increase the temperature of the fuel reformer rapidly, so that the fuel processor is operable within a short time period.
In a further preferred embodiment, the fuel injection nozzle and the spark plug are arranged near the fuel processor inlet and thereby also near the fuel reformer section.
Additionally, it is advantageous to provide an enlarged mantel space in this area because more fuel can be burned, which in turn speeds up the preheating respectively the start up process.
In a further preferred embodiment, a heat exchanger, preferably a counter flow or cross-flow heat exchanger, is arranged downstream of the reformer section, so that heat can be exchanged between the fluid stream of the mantel space and the fluid stream inside the reformer. This is particularly advantageous during the start up process of the fuel processor, where heat, generated by e.g. the ignition of the fuel/air mixture, is transported to the inside of the fuel reformer.
In a further preferred embodiment, for transporting the heat to the inside of the fuel reformer during the start up phase, the fluid streams inside the mantel space and the inner housing are reversed. That means, the fluid stream inside the inner housing has a direction from the fuel processor outlet to the fuel processor inlet and subsequently enters the mantel space through fluid connection openings in the inner housing. Then, the fluid stream in the mantel space is directed from the fuel processor inlet to the fuel processor outlet and exits the mantel space through the fluid inlet in the outer housing.
Since the ignition takes place in the mantel space, such reversed fluid stream ensures that the heat generated by the ignition can be exchanged to the fluid stream inside the inner housing by the heat exchanger. This in turn means that the fluid stream entering the inside of the reformer is preheated by the heat of the ignited fuel/air mixture. As a result, the fuel processor can be brought to its operating temperature in a very short time period.
The reversed fluid flow has the further advantage that soot generated by burning the fuel for the start up process cannot enter the inside of the fuel reformer and contaminate the reformer catalysts as it will be transported to the heat transporting fluid inlet during the start up process. The temperature during the start up process rapidly increases, so that generated soot will be burned away before the fluid flow direction is re-reversed to its operating direction (from fluid inlet to processor outlet). The heat exchanger itself is not affected by soot, since firstly the heat exchanger is made from a material which is insensitive to soot, and secondly accumulated soot will be burned by the operating temperatures of the reformer during the start up process and is transported off.
Even if the inventive method for operating a fuel processor is described in this application in context of a fuel processor, the inventive method can also be used for operating a fuel reformer, only. Thereby the fuel reformer preferably also has a heat exchanger, which is arranged downstream of the fuel reformer, but no subsequent gas cleaning units. Since a fuel reformer itself is also known as fuel processor in the state of the art, the phrase “fuel processor” herein is used for both—a stand alone fuel reformer and a fuel reformer with subsequent gas cleaning unit(s).
In a further preferred embodiment, at least one further heat exchanger is arranged in the mantel space near the reforming section, and/or the gas cleaning section. Thereby, heat generated during operation of the fuel processor can be used for heating the heat transporting fluid and can be transported off so that the temperatures of the different sections of the fuel processor can be controlled.
It should be noted that a fuel processor has a temperature gradient between the fuel processor inlet and the fuel processor outlet. The fuel processor inlet and the fuel reformer section have temperatures above 600° C., wherein the subsequent gas cleaning units have much lower temperatures. For example, a preferential oxidation unit operates at temperature below 200° C. or even below 100° C.
In a further preferred embodiment of the invention, the arrangement of the fluid inlet near the cool fuel processor outlet and the arrangement of the fluid connection openings near the fuel processor inlet provides the possibility to preheat the heat transporting fluid stream by arranging heat exchangers in the mantel space before it enters the hot section of the fuel processor. Introducing hot air to the inside of the inner housing near the fuel reformer unit has the further advantage that an additional pre-heating element for air is not needed.
Additionally, water, which is necessary for the reforming process and also for the cleaning of the hydrogen rich gas from unwanted by-products, can be preheated by the heat transporting fluid for producing steam. The steam production has the preferred side effect that it cools the heat transporting fluid and thereby also the reactor units inside the inner housing. Thereby, the units can be kept on their optimal operating temperature.
Further advantages and preferred embodiments are defined by the description, the figures and the appending claims.